1. Field of the Invention
The present invention relates generally to apparatuses used for fabricating liquid crystal devices and methods of fabricating the same and particularly to driver circuit integrated liquid crystal display devices and methods of fabricating the same.
2. Description of the Background Art
In a driver circuit integrated liquid crystal display device with a thin film transistor (TFT), a TFT in a pixel region only serves to charge a pixel electrode and switch to hold electric charge. As such, it does not require a precisely controlled threshold voltage, as is required for typical semiconductor devices. As such, it can operate satisfactorily with its thin film semiconductor formed of amorphous silicon.
In recent years, there has been developed a technology using a polycrystalline silicon TFT fabricated by laser-annealing amorphous silicon and there have been increasingly fabricated liquid crystal devices using this polycrystalline silicon TFT. Advantageously, the liquid crystal display device of this type has a driver circuit region and a pixel region integrally formed to reduce its fabrication cost and provide the display pixels with high definition. This polycrystalline silicon TFT is required to have a characteristic required for an element of the driver circuit and it is thus required to have a threshold voltage held with high precision. In this situation, a new issue to be overcome has arisen.
A process using amorphous silicon to fabricate a conventional liquid crystal display device normally includes;prior to the amorphous silicon deposition step, a cleaning step to remove foreign matter and provide an amorphous silicon film with an enhanced contact performance. FIG. 12 shows the environment of a conventional route from a cleaning step to a deposition step. The cleaning step includes a physical cleaning step 110 and a chemical cleaning step 120. A substrate 111 mounted in a cassette 106 is input by an automatic guided vehicle (AGV) 140 into a loader 143 and input by a transport robot 104 into a physical cleaning chamber and thus physically washed. The term xe2x80x9csubstratexe2x80x9d herein refers to a substrate per se such as a quartz substrate as well as a processed substrate. Initially, the substrate is irradiated with ultraviolet light output from a UV lamp 151 and thus has organic matter removed therefrom. Then the substrate is sent to a physical cleaning unit 152 and therein cleaned with a brush, megasonically, or in a similar manner. Then the substrate is passed through a water-washing unit 154 and a drying unit 155 and thus delivered into an unloader 145. Chemical cleaning step 120, having a chemical cleaning unit 153 using a chemical for cleaning a substrate, has an inlet and an outlet respectively inputting and outputting the substrate in the same manner as the physical cleaning step. The substrate physically and chemically cleaned is accommodated in cassette 106 open to the atmosphere of a clean room and thus transported to a film deposition chamber 102 by the AGV and input to a loader/unloader 146 thereof, in which substrate 111 is ejected by transport robot 104 from cassette 106 and introduced into the film deposition chamber and subjected to the amorphous silicon deposition step. Then, substrate 111 is again exposed to the atmosphere of the clean room and thus transported to a laser annealing chamber and therein it is laser-annealed to crystallize the deposited amorphous silicon. Waiting until the film deposition chamber is available, such substrates can be disadvantageously forced to be reserved in an inventory 130 and an underlying film thereof can be disadvantageously exposed to the atmosphere internal to the clean room over a long period of time. Conventionally, substrates being transported and reserved have been strictly controlled to prevent particles from adhering thereto.
However, the above substrate, exposed to the atmosphere of the clean room, has a surface insufficiently controlled and thus chemically contaminated. Such chemical contamination does not at all affect an amorphous silicon TFT used only in a pixel region. For a polycrystalline silicon TFT configuring a driver circuit, however, the doping effect of metal contamination or the like and the influence of organic contamination, for example upon the grain growth of polycrystalline silicon appear. Thus, the transistor""s threshold voltage varies, an in-substrate variance occurs and the driver circuit erroneously operates, disadvantageously resulting in a reduced yield.
An object of the present invention is to provide an apparatus manufacturing a liquid crystal display device capable of preventing a chemical contamination attributed to being exposed to an atmosphere internal to a clean room, to prevent a threshold voltage from having a variance or the like, and a method of manufacturing the same.
The present invention provides an apparatus manufacturing a liquid crystal display device, including a cleaning chamber cleaning a substrate of a liquid crystal display device, a film deposition chamber depositing a film on the substrate cleaned in the cleaning chamber, and means for transporting the substrate from the cleaning chamber to the film deposition chamber while preventing the substrate from being exposed to an external atmosphere.
As such, the substrate after it is cleaned is not exposed to the atmosphere of the clean room and it is thus prevented from chemical contamination. This can prevent metal contamination resulting in a doping effect and also prevent organic contamination resulting in the crystal grain size having a variance. As such, a threshold voltage does not vary. Furthermore, the substrate after it is cleaned can be free of particles adhering thereto. As a result, the driver circuit does not erroneously operate and the production yield is thus not reduced. It should be noted that the above substrate is that as previously defined.
In the above present apparatus the means for transporting includes a path blocking an external atmosphere and transporting the substrate from the cleaning chamber to the film deposition chamber, and a transporter transporting the substrate through the path.
As such, the substrate can be readily, automatically transported while it is not exposed to the external atmosphere. Since the substrate can be automatically transported, the substrate does not need to wait for a long period of time and it can also be transported in a reduced period of time. Thus, the device can be manufactured efficiently.
In the above present apparatus the means for transporting includes means for inputting into a sealed cassette isolatable from an external atmosphere the substrate cleaned in the cleaning chamber, while preventing the substrate from being exposed to the atmosphere, and means for outputting in the film deposition chamber the substrate from the sealed cassette.
As such, the substrate is not exposed to the external atmosphere and can thus be accommodated in the sealed cassette and thus transported from the cleaning chamber to the film deposition chamber. Thus, the substrate can be free of chemical contamination and particles adhering thereto after it is cleaned. The sealed cassette may be transported from the cleaning chamber""s unloading portion to the film deposition chamber""s loading portion by means of a transporting machine such as an AGV or manually.
The above present apparatus further includes a cassette load chamber and a transport robot chamber having a transport robot, wherein the cassette load chamber, the cleaning chamber and the film deposition chamber are arranged to surround the transport robot and connected to the transport robot chamber to allow the transport robot to input and output the substrate.
As such, from the cassette load chamber through the cleaning chamber to the film deposition chamber the transport robot can transport the substrate sequentially without exposing the substrate to the external atmosphere. As such, the substrate can be free of chemical contamination and particles adhering thereto after it is cleaned and the film deposition process can be provided rapidly and efficiently. Furthermore, the apparatus having the above each chamber incorporated therein can be miniaturized to save a space in the clean room. In the present apparatus desirably the external-atmosphere blocked path or the sealed cassette has an internal atmosphere depressurized to no more than 103 Pa, for example, an atmosphere of gaseous nitrogen or an atmosphere of dry air. The substrate in the above atmosphere can be free of chemical contamination and particles adhering thereto after it is cleaned and since such atmospheres can be obtained at low cost the production cost is not increased. It should be noted that in the present specification, gaseous nitrogen, dry air and the like will be referred to as an inert gas.
The above present apparatus further includes an annealing chamber connecting to the path and blocked from an external atmosphere, annealing the substrate.
As such, a deposited film can be annealed without being exposed to the external atmosphere. Thus, a deposited amorphous silicon film can be prevent from chemical contamination and the like while it is annealed, and it can thus be provided as a polycrystalline silicon film.
The above present apparatus includes an optical alignment unit capable of laser-annealing the substrate in the annealing chamber.
As such, an amorphous silicon film can be annealed at a low temperature and thus provided as a polycrystalline silicon film having a large crystal grain size. Thus, there can be manufactured a TFT free of chemical contamination and also having a capability allowing the TFT to be used in a driver circuit.
In the above present apparatus the film deposition chamber includes a first film deposition chamber connecting to the path and a second film deposition chamber connecting to the path.
As such, a film deposited in the first deposition chamber that is susceptible to chemical contamination, such as polycrystalline silicon, can be free of chemical contamination on a side thereof opposite to an underlying film as well as on an upper side thereof or a side thereof opposite to the gate insulation film. As such, a stable threshold voltage can be obtained and an increased yield can thus be provided.
In the above present apparatus the path or the cassette is roughly blocked from an external atmosphere to have a loosely sealed structure and it contains a gas inert surrounding the substrate and maintained to have a pressure more positive than the external atmosphere. In this arrangement desirably the apparatus further includes a chemical filter passing and thus introducing the inert gas into the sealed cassette.
The above structure can be implemented less expensively than a tightly sealed structure. As such, chemical contamination and particles adhering to the substrate can be prevented at low cost to further enjoy a further increased yield.
The present invention provides a method of manufacturing a liquid crystal display device, including the steps of, inputting into a cleaning chamber a glass substrate with an underlying film thereon, and cleaning the substrate; outputting the cleaned substrate from the cleaning chamber and inputting the substrate into a film deposition chamber while preventing the substrate from being exposed to an external atmosphere; and depositing an amorphous silicon film on the substrate in the film deposition chamber.
As such, an amorphous silicon film susceptible to chemical contamination can have a lower side free of chemical contamination and particles adhering thereto. As such, the transistor can be free of erroneous operation and a high yield can thus be maintained.
In the above present method the step of depositing is followed by the step of annealing the substrate with the amorphous silicon film deposited thereon while continuing to prevent the substrate from being exposed to the external atmosphere, to provide a polycrystalline silicon film.
As such, in a pixel region a high definition can be achieved and in a driver circuit region the drive transistor can have a high-precision threshold voltage that is inexpensive and stable. Furthermore, the pixel region and the driver circuit region can be integrally formed to allow the liquid crystal display device to be miniaturized, which is important for liquid crystal display devises.
In the above present method the step of depositing is followed by the step of transporting the substrate to another film deposition chamber while continuing to prevent the substrate from being exposed to the external atmosphere and the step of providing a gate insulating film on the polycrystalline silicon film in the another film deposition chamber.
As such, the polycrystalline silicon can have a side opposite to an underlying film and that opposite to the gate insulating film that are free of chemical contamination and particles adhering thereto after the substrate is cleaned. As such, the threshold voltage can be further limited in variation to prevent further yield reduction.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.